The present invention relates to a atomizer that permits forming an aerosol that is rapidly deposited onto a surface, such as a wafer to avoid uneven deposition.
U.S. Pat. No. 5,534,309, discloses a method and apparatus for the controlled deposition of particles on wafer surfaces. In FIG. 3 of that patent an apparatus is shows where electrically charged aerosol particles are introduced into a deposition chamber. An electric field is established above the wafer surface to deposit the charged particles onto the wafer at a rate that is higher than can be achieved without such an electric field. Without an applied electric field, particles can deposit onto the wafer only by the usual mechanisms of gravitational settling and Brownian diffusion. However, these mechanisms are insufficient by themselves to deposit particles at a sufficient high rate onto the wafer for certain applications. To achieve a high deposition rate, it is essential that a source of aerosol particles carrying a high level of electric charge be used, and that the electric field above the wafer be as high as practical to aid in particle deposition.
Although increasing the electric field can increase the rate of deposition, the magnitude of the electric field is limited by electrical break-down in the carrier gas. At atmospheric pressures, if the gas is nitrogen or air, the maximum electric field is limited to 30,000 V/cm in order to avoid sparking or creating a corona discharge. If the applied electric field cannot be increased to a high enough level to achieve an adequate deposition rate, the only recourse is to increase the charge on the particles in order to increase the rate of deposition.
Although aerosol particles produced by atomization usually carry a natural electrical charge, the level of charge is quite low and inadequate for achieving a high deposition rate.